Historically, plastic pouches for food, home or personal care markets were arranged horizontally. However, when these pouches are arranged horizontally, it is difficult for a consumer to determine the contents because the principal display panels are generally concealed. It was therefore desired to develop pouches capable of standing upright for standing on retail shelving so the packaging can be front and center with shoppers and attract the shopper's eyes. Today, such pouches, known as Stand-up Pouches (or “SUPs”), are a common sight throughout the world, and particularly in Asia. These SUPs used for a wide range of end-use applications and also positioned as refill packs for bottles. Different polymers can be used in SUP structures. They can be made to fulfill many demands and requirements
In order to function as a standup pouch, the films used to make the pouch must exhibit sufficient stiffness so that the bags may stand without becoming distorted and losing their shape. Further they must exhibit suitable toughness so that they are not easily ruptured. Additionally, they should be capable of being sealed using the common heat seal equipment used in industry. For some applications it is also desirable that the pouches provide a barrier to moisture, light and/or oxygen transmission.
Currently, most of the SUPs in the market are made with polyethylene (PE) film (mono or coex) laminated with another material to provide stiffness or other desired properties. Often this other material is polyethylene terephthalate (PET). There are also other structures where polypropylene and/or aluminum foil and/or polyamides (Nylon) are used. However, there is no Stand-up-Pouch produced with only polyethylene.
Achieving a film capable of use as a stand-up pouch using only polyethylene resin would be desirable for sustainability purposes. In general, the use of polyethylene would allow companies to down-gauge the film while retaining adequate puncture resistance. This would in turn reduce the amount of energy needed for transporting the packaging materials as well as reduce the volume of waste sent to the landfill. Moreover, a film structure comprising a single class of resin, like polyethylene, can more easily be recycled.
Accordingly, in one embodiment the present invention covers a monofilm structure suitable for use in stand up pouches on its own, without lamination to another film. For purposed of the present invention, “monofilm” means films which are produced in a single production step, such as in an extrusion process. As is known in the art, production processes such as extrusion and coextrusion can produce films having one or more layers, which are “monofilms” for the purpose of this disclosure.
The monofilm of the present invention is a coextruded film, comprising at least three layers. The first surface layer (X) comprised from 50 to 100 percent (by weight of the layer (X)) of a linear low density polyethylene having a density from 0.89 to 0.91 g/cm3 and a melt index of less than 1.3 dg/min, and a peak melting point in a range of from 85° C. to 105° C., and a molecular weight distribution, Mw/Mn range of 2.0 to 3.0.
This monofilm further comprises at least one core layer (Y) comprising from 60 to 100 percent (by weight of the layer (Y)) of a first multimodal polyethylene polymer having a multimodal distribution in terms of molecular weight, wherein said first multimodal polyethylene comprises units derived from ethylene and at least one C3-C10 alpha-olefin (preferably C6-C8), and wherein the first multimodal polyethylene polymer has a density in the range of 0.950-0.965 g/cm3, a melt index of less than 1.20 dg/min, a peak melting point greater than 120° C., and a molecular weight distribution, Mw/Mn ratio greater than 5.0.
The monofilm of the present invention further comprises a second surface layer (Z) which comprises from 50 to 100 percent (by weight of the layer (Z)) of a second multimodal polyethylene polymer having a multimodal distribution in terms of molecular weight, wherein said second multimodal polyethylene comprises units derived from ethylene and at least one C3-C10 alpha-olefin (preferably C6-C8), said second multimodal polyethylene polymer having a density in the range of 0.950-0.965 g/cm3, a melt index of less than 1.20 dg/min, and a peak melting point in the range of from 120° C. to 135° C., and a molecular weight distribution, Mw/Mn ratio greater than 5.0.
The second surface layer (Z) in the monofilm may further comprise from 0 to 50 percent (by weight of the layer (Z)) of a copolymer comprising units derived from ethylene and at least one C3-C10 alpha-olefin (preferably C6-C8), and wherein the polyethylene polymer has a density in the range of 0.91- to 0.95 g/cm3, a melt index of less than 1.2 dg/min, a peak melting point greater than 110° C., and a molecular weight distribution, Mw/Mn ratio greater than 3.0. This component can be multimodal or monomodal.
In another embodiment, the present invention is a laminated film structure suitable for use in stand up pouches comprising a first film and at least a second film laminated to the first film. The first film is a coextruded film comprising at least a surface layer (A) comprising from 70 to 100 percent (by weight of the layer (A)) of a linear low density polyethylene having a density from 0.89 to 0.91 g/cm3 and a melt index of less than 1.3 dg/min, and a peak melting point in a range of from 85° C. to 105° C., and a molecular weight distribution, Mw/Mn range of 2.0 to 3.0. The first film also comprises at least one additional layer (B) comprising from 70 to 100 percent (by weight of the layer (B)) of a first multimodal polyethylene polymer having a multimodal distribution in terms of molecular weight, wherein said first multimodal polyethylene comprises units derived from ethylene and at least one C3-C10 alpha-olefin (preferably C6-C8), and wherein the first multimodal polyethylene polymer has a density in the range of 0.950-0.965 g/cm3, a melt index of less than 1.20 dg/min, a peak melting point greater than 120° C., and a molecular weight distribution, Mw/Mn ratio greater than 5.0.
The second film, which is laminated to the first film in order to form the film structure, is also a coextruded film, but comprises at least three layers. The first surface layer (C) comprises from 60 to 100 percent (by weight of the layer (C)) of a second multimodal polyethylene polymer having a multimodal distribution in terms of molecular weight, wherein said second multimodal polyethylene comprises units derived from ethylene and at least one C3-C10 alpha-olefin (preferably C6-C8), and wherein the second multimodal polyethylene polymer has a density in the range of 0.91- to 0.93 g/cm3, a melt index of less than 1.2 dg/min, a peak melting point greater than 110° C., and a molecular weight distribution, Mw/Mn ratio in the range of from 3.0 to 4.0. The second film also comprises at least one core layer (D) comprising from 70 to 100 percent (by weight of the layer (D)) of a third multimodal polyethylene polymer having a multimodal distribution in terms of molecular weight, wherein said third multimodal polyethylene comprises units derived from ethylene and at least one C3-C10 alpha-olefin (preferably C6-C8), said third multimodal polyethylene polymer having a density in the range of 0.950-0.965 g/cm3, a melt index of less than 1.20 dg/min, and a peak melting point in the range of from 120° C. to 135° C., and a molecular weight distribution, Mw/Mn ratio greater than 5.0.
The second film also comprises a second surface layer (E) comprising from 60 to 100 percent (by weight of the layer (E)) of a copolymer comprising units derived from ethylene and at least one alpha-olefin in the range of C3-C10 (preferably C6-C8), wherein said copolymer has a density from 0.91 to 0.93 g/cm3, a melt index of less than 1.2 dg/min, a peak melting point greater than 110° C. and a molecular weight distribution, Mw/Mn ratio in the range of from 3.0 to 4.5.
The first film and the second film are laminated in such a manner so that the additional layer (B) of the first film is adjacent to the first surface layer (C) of the second film. While other materials than those recited may be blended with the recited materials to form the individual layers, the laminated film structures of the present invention can be characterized it by having no, or substantially no polymer materials which are not characterized as polyethylene homopolymers or copolymers.